Field of the Invention
The present invention relates to a vehicle suspension system and more particularly to a rear suspension system of a motor vehicle.
Conventional independent type vehicle rear suspension systems include a so-called trailing arm type and a semi-trailing arm type. These types of suspension systems include a trailing arm extending in a longitudinal direction of the vehicle body and having a front end attached to the vehicle body for vertical swinging movements, the trailing arm being secured at the rear end to a hub carrier which carries a rear wheel hub. A substantially vertically extending damping strut is provided between the rear end portion of the trailing arm and the vehicle body. The suspension systems of these types are advantageous in that they are simple in structure so that the overall weight can be decreased. There has however been recognized that the suspension systems of these types require trailing arm of substantial cross-sectional area in order to ensure an adequate lateral rigidity. Further, the front end of the trailing arm must be attached to the vehicle body at laterally spaced positions. As the results, the trailing arm must be of a substantial dimension and therefore of an increased weight.
In order to solve the above problems, Japanese laid-open utility model No. 56-62205 proposes, in a vehicle rear suspension system including a trailing arm having a front end mounted on a vehicle body for vertical swinging movements and a rear end carrying a wheel hub, to provide a pair of vertically spaced lateral links which are pivotally connected at the laterally outward ends to the rear end portions of the trailing arm and at the laterally inward ends to the vehicle body. This type of suspension system is advantageous in that the lateral links supports the trailing arm in the lateral direction so that the trailing arm may not be required to possess by itself a substantial lateral rigidity. It should however be noted that in this arrangement there are produced toe-out movements in the wheel when the wheel is bumped upwards with respect to the vehicle body and when the wheel is rebounced downwards with respect to the vehicle body. Such toe-out movements cause a tendency of over-steer in a curved path so that there will be a danger of steering instability.
In the Japanese laid-open patent application No. 60-53408 published on Mar. 27, 1985 and corresponding to the U.S. application Ser. No. 646,070, there is proposed a vehicle rear suspension system which includes a substantially longitudinally extending swing arm having one end pivotably connected with the vehicle body for vertical swinging movements and the other end connected with the wheel hub carrier, and three lateral links extending in substantially lateral directions. The lateral links are pivotably connected at one ends with the vehicle body and at the other ends with the wheel hub carrier at locations which are not aligned on a single straight line. According to the proposed, the three lateral links function to determine the position of the wheel. Therefore, it is possible to prevent or suppress the toe-out displacements in the hump and rebouncing movements of the wheel by properly determining the positions, the lengths and the orientations of the laterial links. It is also possible to control the camber angle of the wheel in a desirable manner.
In the proposed structure, it is advisable to make the swing arm such that it does not disturb the movements of the lateral links. Thus, the swing arm is preferably of a structure having a small rigidity in lateral direction. For example, it may have a very small lateral thickness with a relatively large heigthwise dimension so that it can be easily deflected in the lateral direction. Alternatively or furthermore, the swing arm may be attached to the vehicle body through resilient means such as a rubber bush. It should however be noted that even though the swing arm is constructed to have a small rigidity in lateral directions and mounted on the vehicle body through a resilient rubber bush, the swing arm can still cause a restriction against the swinging movements of the lateral links due to the geometrical arrangements. Since the swing arm conducts swinging movements about the axis of pivotably attachment with the vehicle body, the wheel hub carrier is moved along an arcuate path having the center of arc at the axis of the pivotable attachment in response to the swinging movements of the swing arm. Thus, the lateral links are required to have freedoms not only for vertical swinging movements but also for certain fore-and-aft swinging movements. It should however be noted that it is not easy to obtain a structure which can permit such movements of the lateral links.
Conventional measures for solving the problems are to mount the laterally inner ends of the lateral links through rubber bushes which can allow the fore-and-aft swinging movements of the lateral links. However, such structure is not satisfactory in that the rubber bushes are subjected to substantial torsional and compressive loads which cause complicated deformations of the rubber bushes. As the results, swinging movements of the lateral links are disturbed and the durability of the rubber bushes is adversely affected.